Feature: Allow clients to query InputPlumber over dbus for supported target devices

[pastaq]

As we add additional targets over time we will need to include an updated list on client devices. As clients, such as OpenGamepadUI, can update outside the release cycle provided in immutable OS's like ChimeraOS and Manjaro Gaming Edition. Rather than create a scenario where we're constantly playing catch up, we should just report the available target gamepad devices that a given version has. This will ensure an unsupported target device can't be selected if the client updates before InputPlumber.